To be able to produce paper of a certain quality different chemical additives may be used during the production process. Generally, it is distinguished between process chemicals used to enhance the runnability of the process, and functional chemicals which provide certain properties to the finished paper.
Sizing of paper is used to hinder penetration of water into the sheet. This repellence is needed for durability and other wished paper characteristics like printability. Thus, sizing agents belong to the functional chemical group. Hydrophobation of the fiber can be achieved by a modification of the fiber constitution in the paper. Molecules which are able to attach to the fiber with one side and hinder the penetration of water with the other side are added to the furnish during the papermaking process. When paper is sized in this way it is called internal sizing.
Another way of sizing is to apply the sizing agent only on the surface of already finished paper-sheets. Therefore the paper is coated with a film consisting of a sizing agent, polymer solution and additives. This is called surface sizing.
Due to the increasing use of calcium carbonate as filler modern paper machines are run at a neutral or slightly alkaline pH. This limits the application of rosin or rosin soaps, which are classical sizing agents under acidic conditions.
As it is believed that the common sizing agents for neutral and alkaline sizing react with the hydroxyl groups of the cellulose, they are also called reactive sizes. The most common used reactive sizes are alkyl ketene dimers (AKD) and alkenyl succinic anhydrides (ASA). While the first mentioned shows a reasonable hydrolytic stability the opposite is true for ASA. Consumption of reactive sizing agents is significantly lower than for the rosin sizes.
For ASA-production α-olefins need to be isomerized to form internal olefins. This means the double bond is shifted away from an outward position of the molecule. In a second step the olefine reacts with maleic acid anhydride (MAA) at high temperature. The prior production of the internal olefin is necessary due to the higher melting point of an ASA produced from α-olefin, which means the α-ASA would be solid at room temperature and this would make the application at paper machines quite difficult.
An interest to substitute petrochemical based raw materials with renewable resources is recently observable not only in the paper industry. So a new sizing agent based on green sources can possibly be used to gain market potential. The production of ASA is dependent on petrochemicals (olefin) and therefore its production cost is strongly influenced by the heavily fluctuating price for crude oil.
WO 03/000992 discloses a soybean derived product (PDS size) comprising pure fatty acids extracted directly from soybean oil.
WO 2007/070912 discloses the use of liquid fatty acid anhydrides (FAA) derived from mixtures of saturated and unsaturated fatty acid mixtures with a chain length of C12-C24. The fatty acid anhydride consists of two fatty acids, of a fatty acid and acetic acid, of a fatty acid and a rosin acid, or a mixture thereof. The fatty acid may be derived from tall oil, sunflower oil, rapeseed oil, soy bean oil, linseed oil or animal oil.
WO 2006/002867 disclose yet another alternative sizing agent in the form of a dispersion comprising dispersed in water a sizing agent composed of a reaction product of maleic acid anhydride (MAA) and an unsaturated fatty acid alkyl ester, the sizing dispersion additionally comprising an aluminium compound such as aluminium sulphate, polyaluminium sulphate or polyaluminium chloride.
CA 1 069 410 discloses the use of an emulsifying agent comprising a trialkylamine or ammonium hydroxide in combination with a sizing agent. The sizing agent may be a maleated vegetable oil, maleated α-olefine, maleated fatty ester or AKD.
Maleated oils are well known in the literature for various purposes. According to U.S. Pat. No. 3,855,163 the modified oils are used as additives for electro deposition, while CA 1 230 558 and DE 198 35 330 suggest adding the same to hair care products. According to WO 2005/077996 and WO 2005/071050 maleated vegetable oils are used as emulsifiers. Additionally, US 2006/0236467 teaches that maleated oils are useful in forming latexes, coatings and textile finishes.